It is well known in this art that, in order to improve the impact strength of thermoplastic resins such as ABS type resin or the similar resins, in the preparation thereof, thermoplastic resins such as styrene-acrylonitrile copolymer, polystyrene, polymethyl methacrylate and the like are blended with a graft copolymer. This graft copolymer is prepared by graft copolymerizing rubber latex, that is, diene-type rubber lattices such as polybutadiene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer and the like.
In the U.S. Pat. Nos. 3,509,238 and 4,520,165, the use of water soluble potassium persulphate initiator is described, and the total reaction time is approximately 6 hours. U.S. Pat. No. 4,009,227 describes the use of water soluble initiator and polybutadiene rubber latex having relatively higher gel content of 85%.
However, the resulted thermoplastic resin has relatively lower impact strength, and the total reaction time is more than four hours.
Additionally, U.S. Pat. Nos. 3,928,494, 4,753,988, 4,668,738 and GB 1,501,256 have all disclosed the use of water-soluble initiator.
In these disclosures, however, the total reaction time is more than 5 hours, and the gel content of the used rubber lattices is not described.
In general, the graft polymerization as mentioned above is conducted via emulsion polymerization. It is well known in the art that the graft polymerization generally takes about 5 hours, and that shortening of said reaction time yields an insufficient degree of grafting which leads to lower dispersability when the graft polymer is blended with the thermoplastic resins. Therefore, the resulted thermoplastic resin composition has low impact strength, inferior surface gloss and poor processability due to their lower dispersability.